A common rail fuel injection apparatus is known, which has a common rail commonly used to the cylinders to accumulate high-pressure fuel therein. A fuel supply pump pressure-feeds the fuel to the common rail, and the pressure of the fuel in the common rail is controlled to be a predetermined value. The fuel is injected into the cylinders by driving the injectors on the cylinders at specific timings. In general, the injector for the common rail fuel injection system has a construction to increase and decrease the pressure in a control chamber by actuating a control valve with an actuator, to lift up and down a nozzle needle to open and close an injection hole.
In the injector body, that is, in the body of the injector is formed a high-pressure fuel passage to supply the high pressure fuel from the common rail through a plurality of body members of the injector body to the control chamber and to the injection hole. Thus, it is necessary to secure a sealing performance at intimate contact end faces of the body members. As a general method to securely seal the intimate contact end faces, the end faces of the body members of the injector are processed by finish machining to be flat. The body members are stacked in a longitudinal direction of the injector, and brought into intimate contact with each other by an axial force by a fastening nut, to seal the intimate contact end faces.
However, the above-mentioned method has an issue that quite large axial force is necessary when the sealing pressure is high, and even slight error in the finishing accuracy on the end surface may cause leakage of the fuel. U.S. Pat. No. 4,094,465 discloses an injector having a leakage fuel collection passage for collecting a leakage fuel leaked at the end faces. The leakage fuel collection passage is connected to the fuel return passage to collect the leakage fuel, and arranged to isolate other passages so that the leakage fuel does not flow into other passages.
Further, WO-00-60233-A1 discloses another injector to form a sealing surface. Specifically, an end face of one body member has a flat shape, and an end face of the other body member, which is to be in contact with the one body member, has a depression thereon. Thus, only the end face without the depression forms the sealing surface. The leakage fuel leaked on the sealing surface is collected by a fuel return passage that opens on the end face having the depression.
FIG. 5 schematically depicts the construction of this kind of the injector for the common rail fuel injection system. The injector has: a body member 101 that installs an actuator therein; a plate member 102; a valve body 103 that forms a control valve portion; and a nozzle body 104 that forms an injection nozzle body 104. The body member 101, the plate member 102, the valve body 103 and the injection nozzle body 104 are stacked in a longitudinal direction of the injector, and inserted into a nut 105 to screw-fasten a screw thread 106 to the nut 105 to be one body. Thus, the end faces of the body member 101, the plate member 102, the valve body 103 and the injection nozzle body 104 are brought into intimate contact with each other to be sealed. FIGS. 6A and 6B depict an upper end face of the valve body 103 and a lower end face of the plate member 102 that are in contact with each other. On an approximately entire area on the upper end face of the valve body 103, except an outer circumferential portion 116, a periphery of the high-pressure fuel passage 107 and a periphery of the control pressure passage 108 connected to the injection hole, is formed a depressed portion 109. A low-pressure passage 110 opens to the depressed portion 109.
When the upper end face of the valve body 103 is abutted against the lower end face of the plate member 102, the outer circumferential portion 116 and an annular surface 111 around the high-pressure fuel passage 107 and the control pressure passage 108 on the upper end face of the valve body 103 come in intimate contact with the flat shaped lower end face of the plate member 102. Thus, the high-pressure fuel passage 107 and the low-pressure passage 110 are respectively formed to be continuous passages, the control pressure passage 108 is communicated with a low-pressure passage 113 on the plate member 102. Accordingly, a valve 112, which is installed in the control pressure passage 108, comes in contact with a piston 114, which is installed in the low-pressure passage 113. In FIGS. 6A and 6B, the referential numeral 115 denotes positioning pin holes.
However, in the above-mentioned structure of the conventional injector, the depressed portion 109, which is formed on one of two end faces to come in contact with each other, is under severe design constraint. Especially, the fuel injection pressure is increasing in recent years, so that it is necessary to form a sealing surface to surround the high pressure fuel passage (the annular surface 111 in FIG. 6) with a width of specific length or more, to secure a sealing performance of the high-pressure fuel passage. However, according to this construction, a space between the annular surface 111 surrounding the high-pressure fuel passage 107 and the outer circumferential portion 116 of the valve body 103 is formed to be a quite narrow groove 117, which cannot be easily processed.
This issue occurs on every contact faces between the body members (the body member 101, the plate member 102, the valve body 103 and the injection nozzle body 104) of the injector. In order to form the depressed portion 109 to avoid the many fuel passages required in the injector, it is necessary to form a part of the depressed portion 109 in a quite narrow or complicated shape. This causes an issue to increase man hour to manufacture and manufacturing cost of the injector.